There are more options of course... depends on your preferences. In general there is no problem running an LTR and RTL sites together with the same instance of Kentico.
Kentico CMS automatically supports languages that read from right to left (RTL). A single web site can be created in both LTR and RTL language. Also, Kentico CMS editing interface works correctly with RTL languages.
You can find also some information in the Developers Guide: RTL Languages
and Configuring Multilingual UI
and CSS Ooverview
So when it comes to licensing, you can simply run multilingual websites with RTL and LTR languages on the same domain with a single Kentico license.